1. Field of the Invention
This invention relates to a metal seal.
2. Description of the Related Art
Conventionally, metal seal 41 shown in FIG. 7 is known (refer to Japanese patent provisional publication No. 2009-24838, for example). That is to say, the cross-sectional configuration is U-shaped type, of which thickness dimension T41 is large, having a bottom wall portion 42 and side wall portions 43, an outer face of the end of the side wall portion 43 has a small protruding portion 44 for sealing, and the cross-sectional configuration has a concave groove portion 45 which receives fluid pressure.
When the above-described small protruding portions 44 are pressed to parallel two flat faces 46 and 47 and show sealing function, a press-fit state is made with extremely large contact pressure because the thickness dimension T41 is large.
the metal seal 41 shown in FIG. 7 of which thickness dimension T41 is large may not be used, in case that the material of two flat faces 46 and 47 are brittle or easily damaged or easily deformed. Further, the metal seal 41 of which thickness dimension T41 is large can't be used for the position where the compressive force is small when not pressurized.
The inventor of the present invention therefore made metal seals of which thickness dimension T48 in U-shaped cross section is small as shown in FIG. 8, and repeated many experiments. That is to say, the metal thin seal 48 has a contact small protruding portion 49 on the end of the outer face, and is made with the same small thickness dimension T48.
However, it is revealed that the thin seal 48 has a problem as follows. That is to say, as shown in FIG. 9, when used for sealing between the first member 31 which has a rectangular sealing groove 33 and the second member 32 which has a flat face portion 34, the thin seal 48A in original shape shown by two-dot broken line in FIG. 9, when receiving fluid pressure P is excessively deformed into a configuration 48C shown by a continuous line and press-fit to a flat face portion 34, a bottom face 33A, and a side face 33B of the rectangular sealing groove 33 at five positions Y1, Y2, Y3, Y4, Y5. Although the thin metal seal 48 should be press-fit at three positions Y1, Y5 and Y3 shown in FIG. 9, there is a first problem that the small protruding portions 49, which should have desired sealing function, don't have enough contact pressure when fit to the flat face portion 34 and the bottom face 33A of the sealing groove 33, consequently, total sealing function decreases, because the side wall portions 35 of the U-shaped thin seal 48 are strongly press-fit to the flat face portion 34 and the bottom face 33A.
Further, it is also revealed that the cross-sectional configuration of the thin seal 48 has an unusual shape by plastic deformation shown in FIG. 10 when the thin seal 48 is taken out after the pressure-receiving state as shown in FIG. 9. That to say, an original shape 48A shown by a two-dot broken line in FIG. 10 changes into a shape shown by a continuous line because of plastic deformation. Thus, there is a second problem that the small protruding portions 49 can't fit to the flat face portion 34 and the bottom face 33A with enough contact pressure when plastic deformation occurred. Therefore, fluid leakage occurs and the thin seal 48 can't be used and life is short after comparatively short period of use time under used condition in which fluid pressure P changes up and down.
It is an object of the present invention to provide a metal seal with which the above mentioned problems are resolved, which can be compressed by small force, used for a portion where the fastening force, making the parallel two faces close is small, not generating unusual deformation (plastic deformation) under the pressure-receiving state by the fluid pressure, and having stable sealing function for a long period of use. Especially, it is an object to provide a metal seal which has stable sealing function for a long period of use at a used portion where the fluid pressure changes high and low, or where two flat faces repeatedly open and close, and repeatedly slight press-fit and release.